The present invention relates to a cleaning device in general, and more particularly to a device for cleaning a surface, which is equipped with a brush which picks up dirt from the surface to be cleaned and deposits it into a dirt-collecting receptacle.
There are already known various cleaning devices of the type here under consideration. Usually, they include a housing in which wheels are mounted for rotation, such wheels engaging the surface to be cleaned, during the use of the cleaning device for cleaning the surface. At least one cylindrical brush is mounted in the housing for rotation about its longitudinal axis, the brush extending transverse of the direction of movement of the device over the surfface and being parallel to the latter. The aforementioned wheels, or at least some of them, drive the cylindrical brush into rotation about the longitudinal axis thereof so that the bristles of the brush, which contact the surface to be cleaned, pick up dirt therefrom and deposit the same into receptacles which are mounted in the housing alongside the cylindrical brush. The housing of the cleaning device is usually equipped with a handle adapted to be grasped by the user of the device so that the movement of the handle results in a corresponding movement of the device over the surface to be cleaned.
A cleaning device of this type is already known in which the wheels are mounted in the lateral portions of the housing when considered in direction of movement of the device over the surface to be cleaned, and the rotation of the wheels is converted into the rotation of the cylindrical brush in that frictional or gear-type engagement is accomplished between the wheels mounted at the opposite lateral sides of the housing and the longitudinally opposite end portions of the cylindrical brush. This arrangement is completely satisfactory so long as the cleaning device is to be moved over the surface only in a straight path or in straight path portions. Under such circumstances, the angular speeds of rotation of the wheels arranged at the opposite sides of the housing are the same so that the cylindrical brush will be driven into rotation at the same speed by the wheels at one lateral side of the housing as by the wheels arranged at the other lateral side of the housing. However, the situation is quite different when it is desired to move the cleaning device over the surface to be cleaned along a curved path, a situation which is unavoidable when the cleaning device is to be used for removing dirt from corner regions of the surface. So, for instance, when such a cleaning device is to be used for cleaning floors, movement thereof along a curved path is necessary for removing dirt from regions along the baseboards, and particularly in the corner regions of the room and along the bases of furniture pieces standing on the floor. It will be appreciated, however, that when the cleaning device is used for a different purpose, that is, for cleaning surfaces other than floors, similar problems will also be encountered.
The difficulties encountered in these conventional cleaning devices in which the cylindrical brush is driven into rotation at both ends thereof from wheels mounted in lateral portions of the housing, are attributable to the fact that when the cleaning device moves along an arcuate path, the driving wheel which is closer to the instantaneous pole of the curved path than the other wheel rotates at a lesser speed than the wheel which is more spaced from the instantaneous pole. The difference between the speeds of rotation of the wheels mounted at the opposite lateral sides of the housing will be proportionate to the instantaneous radius of curvature of the curved path.
In view of the fact that the wheels mounted at opposite lateral sides of the housing are in driving engagement with the one-piece cylindrical brush, the wheels at one side of the housing will attempt to drive the brush at a higher speed than the wheels at the other side. Therefore, not only will the differential speeds of the wheels to the two sides of the housing result in subjection of the brush to additional torsional stresses but, in the final analysis, the slower-moving wheels will retard the rotation of the faster moving wheels, there will be slippage between the wheels and the surface to be cleaned, and the overall cleaning effectiveness of the cleaning device will be diminished during the movement thereof in a curved path. An additional disadvantage is to be seen in the fact that, when it is desired to move the cleaning device in a curved path, a much higher force must be applied to the device in order to move it over the surface to be cleaned than for moving the device in a straight path, this being attributable to the need for overcoming the frictional engagement of the wheels with the surface to be cleaned in order to achieve the necessary slippage.
This problem has already been recognized, and it has been proposed to overcome this disadvantage by providing a brush in which the shaft of the brush is constituted by coaxial sections, so that the sections of the brush can rotate at different speeds during the movement of the device in a curved path. However, in all of the heretofore known cleaning devices of this type, the construction of the shaft of the cylindrical brush of several sections resulted in reduction in the cleaning effectiveness of the cleaning device, and in a substantial increase in the force which is needed for moving the cleaning device over the surface to be cleaned, at least during the movement of the cleaning device along a curved path.